When US President Joe Biden meets world leaders at a lavish Italian resort this week he will be shadowed by an invisible and, for now, uninvited guest: Donald Trump. The G7 summit in Puglia comes just five months before a nail-biting US presidential election that is not only testing America’s democracy but also causing huge uncertainty for its allies. Hanging over the leaders is the knowledge that it could be the 81-year-old Biden’s last G7, and that Trump, with his America First policies and scorn for international organizations, could be on his way back.